1. Field of the Invention
The present invention relates to a fan driving circuit, and particularly to a fan driving circuit which stabilizes running of a fan.
2. Description of Related Art
Developments in today's highly information-intensive society have led to remarkable improvements in performances of electronic devices. During operation of many contemporary electronic devices such as central processing units (CPUs), large amounts of heat are produced. Typically, an electric fan is used to facilitate removal of the heat. The fan must run stably, so as to prevent the device from becoming unstable or being damaged. A driving circuit accompanying the fan is quite important to ensure normal running of the fan.
FIG. 2 shows a conventional driving circuit of a fan. A Pulse-Width Modulation (PWM) signal from a controlling integrated circuit (IC) drives transistors Q70 and Q100. The transistors Q70 and Q100 directly drive the fan. A high capacity electrolytic capacitor C63 is provided for wave filtering. But when a duty cycle of the PWM signal from the controlling IC is low, the transistor Q100 is turned off and causes fan failure.
What is needed, therefore, is to provide a driving circuit which can run a fan stably even if the duty cycle of the PWM signal is low.